(a) Field of the Invention
The present invention relates to a Electrically-conductive barium sulfate filler and a method for preparing the same and more particularly to a electrically-conductive barium sulfate filler which is excellent in whiteness, non-poisonous and inexpensive, and has electrically-conductivity stable to any temperature change and is highly dispersible in plastics, rubbers, resins, paints and varnishes and fibers as well as a method for preparing the filler.
(b) Description of the Prior Art
Electrical insulating properties of plastics become causes of various technical problems in several applications thereof. The electrical insulating properties of plastics become obstacles in, for instance, shielding electric parts from a relatively high electromagnetic field, for instance, observed when a computer housing is employed or in discharging of electrically-charged parts. The electrical insulating properties of plastics become causes of various problems encountered when storing or conveying high performance explosives or IC parts, preparing carpets which are subjected to an antistatic treatment or rubber products for medical use, or preparing electrically-conductive adhesives for metals.
It has been known that a polymer can be converted into a electrically-conductive material through incorporation of electrically-conductive particles. As fine substances capable of imparting electrically-conductivity to, for instance, plastics and paints and varnishes through incorporation thereof into these substances, there have been known, for instance, metal particles or carbon black particles; particles of semiconductive oxides such as zinc oxide and iodides (e.g., copper iodide); tin oxide powder doped with, for instance, antimony; zinc oxide powder doped with, for instance, aluminum or powder of, for instance, titanium dioxide and aluminum oxide coated with tin oxide; and fibrous materials such as glass fibers, alkali metal titanate fibers and titanium oxide fibers coated with tin oxide.
If metal particles or carbon black particles are used as electrically-conductive particles, polymers are blackened by the addition of such additives, This is often undesirable in most of applications thereof. For instance, the use of zinc oxide particles suffers from a problem that the resulting polymer shows reduced chemical resistance and fluctuation of in the electrically-conductivity due to temperature and/or humidity changes. A polymer comprising copper iodide has very low chemical stability and this substantially limits the application of the polymer. Moreover, antimony-doped tin oxide powder is excellent In a electrically-conductivity-imparting ability, but the resulting polymer has a blue-black color tone due to the doped antimony and suffers from a problem of low whiteness. Further antimony suffers from a problem of toxicity. Thus, the polymers comprising antimony-doped tin oxide powder are substantially limited in the application thereof.
Japanese Un-examined Patent Publication No. Sho 56-157438 discloses a method for preparing a powdery mixture which can be incorporated into plastics to impart electrically-conductivity thereto. This method comprises adding a solution comprising SnCl.sub.4 and SbCl.sub.3 to a heated aqueous suspension of barium sulfate. In this method, the precipitation reaction is carried out in an acidic environment and accordingly, the resulting powdery mixture comprises SnO.sub.2 powder and barium sulfate powder. However, plastics to which such a powdery mixture is added have electrically-conductivities unstable to temperature changes. In addition, the powdery mixture has relatively low dispersibility in plastics and, therefore, it is difficult to uniformly disperse the powdery mixture in the plastics.
As has been discussed above in detail, the conventional electrically-conductive barium sulfate fillers are limited in the application due to insufficiency in at least one of whiteness, transparency, nontoxicity, cost, electrically-conductivity, dispersibility and the like or they are insufficient in at least one of whiteness, transparency, cost, electrically-conductivity, dispersibility and the like.